1. Field of the Invention
The present invention is related to delay-based circuits for measuring metrics such as circuit environment variables, and more particularly to circuits and methods that correct metric measurements made by delay-based circuits.
2. Description of Related Art
Delay-based measurement circuits are finding application in integrated circuits such as processor cores, in which it is useful to evaluate and/or monitor variation in circuit environment metrics such as temperature and supply voltage. Not only do such metrics vary for an integrated circuit external environment, but variations across a die can lead to substantial changes in circuit performance. Therefore, it is useful to make measurements both to evaluate a design and to ensure proper operation of an integrated circuit in the end application. Further, such delay-based measurement circuits are useful as sensor devices, where the application is to monitor a condition such as voltage, current or temperature in an electronic system or temperature in general.
Delay-based measurement circuits are desirable for circuit integration, as they do not require any special process techniques, are compact and are easily designed. Typically, an inverter chain is used to generate a one-shot delay or is connected in an inverting ring configuration to form a ring oscillator. The delay of the one-shot delay or the frequency of the ring oscillator is then measured to yield a measure of a metric to which the delay circuit is sensitive, such as supply voltage or temperature.
However, when multiple circuit parameters of the delay circuit are varying, variation in parameters other than the circuit metric being measured causes error in the measurement. For example, a delay circuit may be used to measure temperature, but if the supply voltage provided to the delay circuit varies substantially, the supply voltage variation introduces error in the temperature measurement. Further, the sensitivities and offset of the delay circuits vary widely by process, to a degree that approaches or even exceeds the variation of delay with the circuit metric being measured.
Therefore, it would be desirable to provide a delay-based metric measurement circuit having improved accuracy and process variation independence. It would further be desirable to provide a delay-based metric measurement circuit that can measure multiple circuit metrics and provide for more accurate measurements of each metric, with low circuit-to-circuit and/or die-to-die variation.